1. Field of Invention
This invention relates to measurement systems involving force or location, in particular to strain-based systems where a force is exerted on an L-beam having an unknown location and/or an unknown force.
2. Description of the Related Art
Stress measurement systems are known in the related art; some non-exhaustive examples are U.S. Pat. Nos. 2,597,751, 3,724,575, 4,858,475, 4,936,149, and 5,837,946. However, systems in the related art suffer from mechanical complications, inaccurate results caused by off-level condition, fragility, imprecision, and are often difficult to install or retrofit.
Vertical-shear-based systems are typical of the current state of the related art. An example is the Routeman refuse truck fork by Vishay. This system is used since the shear load is not affected by placement of the weight on the fork so long as it is actually on the fork distal to the sensor itself. Such vertical shear forces however are small compared to the primary forces of bending in the cantilever beam, and fragile load cells with means to allow vertical displacement of the cantilever beam are used to create the weigh system. Such vertical-shear-based systems generally lack a weigh system using the strain existing in the functional structure. A bending beam-type system captures the primary structural strain to overcome the complexity and fragility of vertical-shear-based systems.
Bending beam systems are known. For example, U.S. Pat. No. 3,724,575 to Kutsay discloses obtaining a weight in the vertical direction by resolving two load cells with sensors along a horizontal beam. However, such bending beam systems have strain gauges inside an elongated hole within a beam, which weakens the beam. Another problem with such bending beam systems is that the sensors are placed closer to the neutral axis of the beam, and since the magnitude of stress approaches zero close to the neutral axis, stress measurements are thus less accurate. In particular, Kutsay does not teach or fairly suggest providing for off-level compensation or location of the load on the bending beam, and is thus not well suited for use on a vehicle.
A beam form is disclosed in U.S. Pat. App. Pub. No. 20060124365 to Coleman is incorporated by reference herein.
It can be seen, therefore, that there is a need to increase accuracy by measuring larger bending strain, rather than smaller shear strain. It can be seen that there is also a need for greater accuracy in weighing an object by improving accuracy in stress measurement. Also, it can be seen that there is a need to improve accuracy by having a sensing system that tends to avoid the neutral axis of the beam. In addition, it can be seen that there is a need for a robust, lightweight sensing system that is less cumbersome or prone to breakage than conventional shear-based systems. Further, it can be seen that there is a need to determine location of a load relative to the system. In addition, it can be seen that there is a need for a mechanically simpler device which can be easier to install or retrofit onto existing systems. It can also be seen that output difference between tensile and compressive stresses can be used to compensate for off-level condition. Additionally, it can be seen that there is a need to resolve a weight or force without knowing or controlling its location on the weighing apparatus. Furthermore, it can be seen that there is a need to determine load of a mass on a beam which can provide measurements to determine threshold weight, costs, fees, or other business conditions. It can be seen that there is a need to determine location or placement of a load on a cantilever beam so as to alert an operator or manager as to various risks, such as load or vehicle tipping, or if a pallet being moved in a loading dock is too far off-center. Finally, it can be seen that there is a need to address a combination of the above problems.